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Upstream energy use in producing and supplying the fuel or electricity (this and on-site energy give primary energy use for the operation of the vehicle, which is what is given in the preceding two slides)

The energy used to make the vehicle (embodied energy), averaged over the total distance travelled during the lifetime of the vehicle

The energy used to make and maintain the infrastructure for the vehicles (roads, rail lines, airports), averaged over the total distance travelled during the lifetime of the vehicle

Making is more practical and economical to serve the reduced travel demand with high-quality (i.e., rail-based) public transit

Increasing the viability of walking and bicycling

Once people start using transit, there is a further reduction in travel demand (in the distances travelled) because people start planning their trips to be more efficient (i.e., combining errands in one trip)

Spark ignition (SI) – runs on gasoline, with power output reduced by reducing the flow of fuel and throttling (partially blocking) the airflow, causing a major loss of efficiency at part load (which is the typical driving condition)

Compression ignition (CI) – runs on diesel fuel, which is ignited by compression without the need for spark plugs. More efficient than SI engines due to absence of throttling, high compression ratio and lean fuel mixture (high air:fuel ratio)

Internal combustion engine (ICE) – refers to engines where combustion occurs in cylinders. Both SI and CI engines are ICEs

Aggressive transmission management – running at optimal gear ratio at all times, which makes the engine operate at the torque-rpm combination that maximizes the engine efficiency for any given driving condition.

Smaller engines (most of the time the engine operates at a small fraction of its peak power). 10% smaller saves 6.6% in fuel because the engine on average will operate more efficiently

Variable valve control instead of throttling of air flow in gasoline engines – saves up to 10%

The energy flow to the wheels increases from 14.8% to 22.7% of the fuel input

Thus, for the same energy flow, we need only 14.8/22.7 = 0.652 as much fuel (a savings of 34.8%)

The loads on the wheels (due to reduced rolling and aerodynamic resistance and reduced vehicle weight) drop from 429.9 kJ/km to 298.0 kJ/km, so the fuel requirement from this alone would be multiplied by 298.0/429.9 = 0.693 (a savings of 30.7%)

The overall fuel requirement is multiplied by 0.652 x 0.693 = 0.452 (a savings of 54.8%, which is < 34.8+30.7)

Cross-check: the ratio of fuel inputs at the tops of the two figures is 1302/2882 = 0.452

The idea here is to recharge the battery from the AC power grid (i.e., by plugging it in when parked) and using the battery until the battery energy drops, then switching to the gasoline (or diesel) engine

This requires batteries with greater storage capacity than in HEVs, giving 40-60 km driving range on the battery

Since most trips are shorter than this, a large portion of total distance travelled could be shifted to electricity in this way

The key issues are the cost of the battery, the mass of the battery (cars with heavier batteries will need more energy for acceleration and climbing hills), the amount of energy stored (usually represent in Wh), which determines the driving range, and the peak power output from the battery (W), which determines how fast the vehicle can accelerate

Fuel cells suitable for use in cars need to be able to operate at low temperature (120ºC)

Low-temperature fuel cells require precious-metal catalysts (Pt and ruthenium) in order to operate (these catalysts are also needed in 3-way catalytic converters, but would not be needed for such in H2 FCVs)

Supplies of Pt are quite limited – the availability of Pt could be a significant constraint on the long-term viability of H2 FCVs

Hydrogen could instead be used in ICEs (with much less pollution), but with only a 10-20% efficiency gain – so the problem of being able to store enough H2 onboard in order to get a reasonable driving range would arise

A vehicle fleet reaching 5 billion (which would result from a human population of 10 billion with European levels of car ownership) and consisting entirely of FCVs would have a cumulative Pt demand by 2100 equal to the upper limit of the estimated amount of Pt that could be mined

This leaves no room for other uses of Pt (such as in jewelry and electronics)

Direct use of renewably-based electricity to recharge batteries makes far better use of the renewable electricity than using it to make H2 to for use in a fuel cell (extra steps mean extra losses)

The land area required to convert sunlight to H2 and drive a given distance is ~ 20 times less than growing biomass to make methanol for use in a fuel cell, or ~ 40 times less than growing biomass to make ethanol

This is because the efficiency of PV modules (~15 % or more) is vastly greater than the efficiency of photosynthesis (~ 1%)

Thus, the best bet seems to move to plug-in hybrid vehicles that are recharged with solar- or wind-generated electricity, with maybe a small amount of hydrogen as a range extender in order to eventually get completely off of fossil fuelsLiquid biofuels would be a distant second best as a range extender, but might be needed if problems with H2 cannot be resolvedSwapping the battery for a freshly charged battery every 100 km might be another solutionIn any case, the underlying vehicle should be as efficient as possible to minimize the electricity and/or hydrogen or biofuel requirements.

Energy use to move people by cars is ~ 2.5 MJ/person km with 1 person per car, and projected to be ~ 1 MJ/person-km with advanced future vehicles (~ 0.25 MJ/person-km if you pack 4 people into the car)

The energy required in today’s high speed trains is ~ 0.08 to 0.15 MJ/person-km

The savings are not quite as large as they appear to be, because high speed trains use electricity which will typically be generated at an efficiency of only 35-40%

So, divide the (electrical) energy use by the train by (0.35 to 0.4 times the transmission and transformer efficiencies) to get fuel use at the powerplant that generates the electricity

Compare this with the amount of crude oil needed to produce the gasoline energy that is saved when people switch to trains. This will be the saved gasoline divided by the efficiency in making gasoline from oil, about 0.85

The thrust generated by the engine is equal to the product of mass x velocity of the air thrown behind the engineDoubling the mass of air thrown and cutting its speed in half gives the same thrust, but much less kinetic energy (which varies with v2) needs to be added in this caseThus, the engine needs to do less work while producing the same thrust

The big improvement has been in thrust specific fuel consumption (TSFC) – decreasing by about 50% for long-haul aircraft from 1959 to 1998, achieved in part through development of engines with larger bypass ratios

Turboprop aircraft have about 20% smaller TSFC than turbofan aircraft

No trend in lift/drag ratio – improvements in overall aerodynamics have offset the impact of fatter engines with larger bypass ratios

A slight upward trend in ratio of empty to full weight – related in part of extra in-flight entertainment systems

Elimination of idling in heavy trucks (averages about 2400 hours/year) through use of auxiliary power units such as fuel cells for air conditioning and other loads (high-temp fuel cells, not requiring Pt catalysts, could be used)

The International Maritime Organization has identified measures that could be phased in and which would reduce shipping energy intensity by 37% over 20 years and by 45% over 30 years

Small wind turbines on a vertical axis (Flettner rotors) fitted to ships and connected to propellers could potentially reduce the remaining energy requirement by 30-40% (already used by the German wind turbine manufacture Enercon on the barges used to transport its offshore wind turbines to where they are installed)

With the inevitable increase in fuel costs and a reduction in the differences between countries, the trend toward ever greater trade may very well be reversed, thereby contributing to reduced freight transportation energy use

Conscious effort by consumers to buy locally-produced products can also contribute to this